Airbag modules consist of casings that comprise a folded bag, which inflates very quickly with gas from a generator after certain sensor devices detect a vehicle collision. This way, the bag unfolds in front of the driver or passenger, depending on location, and prevents their bodies from banging against any part of the vehicle.
In order to prevent the bag from being very rigid in its contact with the driver or passenger, acting as a ball and making the bounce off to cause an excessive impact to the person it unfolds on, they have been equipped with a ventilation orifice that serves to reduce the frontal pressure of the bag and, therefore, the possibility of causing damages when they are operated.
Furthermore, several methods have been used to close the gas discharge orifice and improve pressure control inside the bag than that offered by the variation in size of the orifice.
Using a sealing patch, it is possible to prevent the gas from immediately leaving through the discharge orifice, and only when the patch breaks.
Technology has proposed different types of patches with different means to control their breaking depending, to a greater or lesser extent, of a given resistance to gas pressure inside the bag. This makes the presence of gas pressure necessary for the bag to fulfil its protection function compatible with the guarantee that the gas pressure shall not be excessive, with the consequent risk to persons the bag unfolds for.
Fabric patches have been proposed such as those described in U.S. Pat. No. 3,879,057, U.S. Pat. No. 4,097,065 and U.S. Pat. No. 5,018,761, which have not been successful due to the lack of uniformity of their breaking pressure as a result of their nature.
Plastic patches such as those in U.S. Pat. No. 3,573,885 have also not been successful due to the difficulty of controlling rupture pressure due to the variability of mechanical characteristics in plastic at different temperatures.
In this sense, it is currently considered that patches comprising elastic membranes such as silicone are the most suitable due to the good stability of the material to changes in temperature. Patches are used for varying shapes and thicknesses to control breaking pressure in order to optimize the vehicle occupant retention conditions. A good example is the one described in patent request EP 1022198.
The breaking pressure of a membrane is determined by the size of the sealed ventilation area, hardness of the material involved and its thickness, which may be constant or variable. This implies that airbag module manufacturers require a large variety of patches, both in terms of diameter (if, as is normal, circular patches are used) and thickness, in order to attend to the various types of airbag modules, making it difficult to standardize their production, which hinders the manufacturing of bags.
This invention is targeted to resolve this inconvenience.